1. Field of the Invention
The present invention generally relates to a hydrocarbon fuel reformer and more particularly to a reformer for reforming hydrocarbon fuel to a hydrogen-containing gas.
2. Description of the Prior Art
Conventionally, it has been proposed to use a type of reformer which is filled with alumina pellets carrying a partial oxidation reaction catalyst for oxidizing a portion of hydrocarbon fuel and other alumina pellets carrying a water vapor reforming reaction catalyst for reforming hydrocarbon fuel to hydrogen-containing gas with water vapor (Japanese Patent Laid-Open Publication No. Hei 4-313339 etc.). In this type of reformer, by filling one reaction layer with both alumina pellets carrying partial oxidation reaction catalyst and alumina pellets carrying water vapor reforming reaction catalyst, the necessary heat for the water vapor reforming reaction, which is an endothermic reaction, is obtained by oxidizing a portion of the hydrocarbon fuel to efficiently perform the water vapor reforming reaction. When methanol is used as the hydrocarbon fuel, the water vapor reforming reaction is represented by equation 1 and the partial oxidation reaction is represented by equations 2 to 4. In addition, reactions represented by equations 5 and 6 may also be present in the reformer.
CH3OH+H2Oxe2x86x92CO2 
+3H2xe2x80x83xe2x80x83(1) 
CH3OH+1.5O2xe2x86x92CO2 
+2H2Oxe2x80x83xe2x80x83(2) 
CH3OH+0.5O2xe2x86x92CO2 
+2H2xe2x80x83xe2x80x83(3) 
CH3OH+O2xe2x86x92
CO+2H2Oxe2x80x83xe2x80x83(4) 
CO2+H2xe2x86x92
CO+H2Oxe2x80x83xe2x80x83(5) 
H2+0.5O2xe2x86x92H2Oxe2x80x83xe2x80x83(6)
However, because these reformers were filled with alumina pellets carrying the catalysts, there was a problem that the area and resistance of flow path for the gas which affect the reaction efficiency of the oxidation reaction and water vapor reforming reaction of hydrocarbon fuel cannot be freely designed. This problem can be solved to some extent by considering the shape and size of alumina pellets, but the degree of freedom is still limited.
One of the objectives of a hydrocarbon fuel reformer according to the present invention is to increase the degree of freedom of the design of the reformer with respect to area and resistance of flow path of the gas which affect the reaction efficiency of the oxidation reaction and water vapor reforming reaction of hydrocarbon fuel. Another objective of the hydrocarbon fuel reformer of the present invention is to increase the reaction efficiency of the water vapor reforming reaction.
In order to solve at least some of the objectives mentioned above, the present invention employs the following.
A hydrocarbon fuel reformer according to the present invention is a reformer for reforming hydrocarbon fuel to hydrogen-containing gas, comprising a monolith catalyst carrying a partial oxidation reaction catalyst for oxidizing a portion of the hydrocarbon fuel and a water vapor reforming reaction catalyst for reforming the hydrocarbon fuel to the hydrogen-containing gas using water vapor on a monolith carrier formed from a plurality of cells which separates a gas flow path into a plurality of paths.
In the hydrocarbon fuel reformer of the present invention, because the monolith catalyst is formed by carrying a partial oxidation reaction catalyst for oxidizing a portion of the hydrocarbon fuel and water vapor reforming reaction catalyst for reforming hydrocarbon fuel to hydrogen-containing gas using water vapor on a monolith carrier formed from a plurality of cells for separating a gas flow path into a plurality of paths, by considering the cell shape and cell size, the degree of freedom of the design with respect to the area and resistance of the flow path of gas which affect the reaction efficiency can be improved compared to reformers filled with pellets carrying the catalysts.
In the hydrocarbon fuel reformer of the present invention, the partial oxidation reaction catalyst and the water vapor reforming reaction catalyst can be copper-zinc catalysts. The copper-zinc catalysts act both as a partial oxidation reaction catalyst and a water vapor reforming reaction catalyst, allowing simultaneous carriage of both the partial oxidation reaction catalysts and the water vapor reforming reaction catalysts on the monolith carrier.
In the hydrocarbon fuel reformer of the present invention, the monolith carrier can be a carrier formed from 600 to 3400 cells per square inch and more preferably, it can be formed from 900 to 3000 cells per square inch. In this manner, the water vapor reforming reaction can be performed more efficiently.
Moreover, in the hydrocarbon fuel reformer of the present invention, the monolith catalyst can be formed with the ratio of the length of the gas flow path to the cross sectional diameter of the gas flow path between 5 and 18, and more preferably, it can be formed with the ratio of the length of the gas flow path to the cross sectional diameter of the gas flow path between 8 and 15. In this manner, the water vapor reforming reaction can be performed more efficiently.
In the hydrocarbon fuel reformer of the present invention, the monolith carrier can be formed so that the cross sectional shape of the plurality of cells is a hexagon. In this manner, the water vapor reforming reaction can be performed more efficiently.
Furthermore, in the hydrocarbon fuel reformer of the present invention, the monolith carrier can be formed with at least the flow-in section of the gas flow path formed from a material with low thermal conductivity or from a material with lower thermal conductivity than the other portions. In this manner, the water vapor reforming reaction can be performed more efficiently. In the hydrocarbon fuel reformer of this aspect of the present invention, the monolith carrier can be formed with 2 to 20% of the length of the gas flow path from the flow-in end formed by a material of low thermal conductivity and other portions formed by a material of higher thermal conductivity than the material forming the flow-in end.
In addition, in the hydrocarbon fuel reformer of the present invention, the hydrocarbon fuel can be methanol and the reformer can comprise a methanol supplier for supplying methanol to the monolith catalyst and an oxygen-containing gas supplier for supplying oxygen-containing gas to the monolith catalyst so that the molar ratio of the oxygen atom to the supplied methanol molecule is between 0.1 to 0.42. In this manner, necessary heat for the water vapor reforming reaction can be efficiently obtained from the partial oxidation reaction.
With the hydrocarbon fuel reformer according to one aspect of the present invention which uses methanol as the hydrocarbon fuel, the hydrocarbon fuel reformer can further comprise a water vapor supplier for supplying the water vapor to the monolith catalyst so that the molar ratio of the water molecule to the methanol molecule is at least 1.0. In this manner, the water vapor reforming reaction can be performed more efficiently.
Moreover, with the hydrocarbon fuel reformer according to one aspect of the present invention which uses methanol as the hydrocarbon fuel, the partial oxidation reaction catalyst and the water vapor reforming reaction catalyst can be copper-zinc catalyst. The monolith carrier can be a carrier formed from 900 to 3000 cells per square inch. The monolith catalyst can be formed to make the ratio between the length of the gas flow path and the cross sectional diameter of the gas flow path between 8 and 15. The monolith carrier can be formed by using a material with a low thermal conductivity for 2 to 20% of the length of the gas flow path from the gas flow-in end and a material with a higher thermal conductivity than the material used for the section from the gas flow-in end for the other portions.